Endoplasmic Reticulum and Golgi Body

The organelle, endoplasmic reticulum, which can be seen as present in almost all eukaryotic cells is an organelle that consists of two subunits – SER(smooth endoplasmic reticulum) and RER(rough endoplasmic reticulum). These organelles in rough endoplasmic reticulum form cisternae, a mesh of interconnected, flattened membrane-enclosed sacs, and SER exist as tubular structures. With an exterior nuclear membrane, endoplasmic membranes are continuous. However, these organelles are not present in spermatozoa or red blood cells.

Golgi apparatus was discovered by Camillo Golgi, in the year 1950. It is also called a Golgi Complex or Golgi body, the membrane-bound organelle of eukaryotic cells (cells with clearly defined nuclei) that is made up of a series of flattened, stacked pouches called cisternae. The Golgi apparatus functions to transport, modify, and pack proteins and lipids into vesicles for delivery to targeted destinations. It is placed in the cytoplasm next to the endoplasmic reticulum and near the cell nucleus. While many types of cells contain only one or several Golgi apparatus, plant cells can contain hundreds.

The Function of Golgi Apparatus

Golgi apparatus performs various important functions inside the cell like:

(i) The main function of the Golgi apparatus is to carry out the processing of proteins generated in the endoplasmic reticulum. Golgi apparatus also transports protein to the different parts of the cell.

(ii) The modification of cargo proteins is carried out by the Golgi enzymes present in membranous disks of cisternae. Modification of various substances is carried out by enzymes in cisternae with the help of processes like phosphorylation and glycosylation.

(iii) Nucleotide sugars are imported by the Golgi apparatus from the cytosol to carry out the glycosylation and phosphorylation processes. 

(iv) Polysaccharides are attached with proteins in order to form care) One of the tasks of the Golgi apparatus is carrying out the breakdown of proteins and the formation of small, active fragments. carbohydrates.

(v) One of the tasks of the Golgi apparatus is carrying out the breakdown of proteins and formation of small, active fragments.

(vi) Sulfate groups are put to protein molecules in the Golgi apparatus.

(vii) Adding phosphate molecules onto molecules of proteins is also a vital task carried out in the Golgi apparatus.

(viii) Transfer of lipids around cells and creation of lysosomes are the vital functions carried out by the Golgi apparatus.

(ix) The Golgi body carries out the synthesis of proteoglycans. The proteoglycans are found in the extracellular matrices of animal cells.

(x) Carbohydrates are synthesized in the Golgi body. The process of carbohydrate synthesis involves the production of polysaccharides and glycosaminoglycans (GAGs).

MCQs

1. The Place where the process of Detoxification of Xenobiotic Compounds occurs

(a) Rough Endoplasmic Reticulum

(b) Ribosomes

(c) Cytosol

(d) Smooth Endoplasmic Reticulum

Answer: (d)

2. This is the function of Glycosylation

(a) Helps in cell-cell adhesion

(b) Confer stability in proteins

(c) Helps in the proper folding of the protein

(d) Synthesis of membrane lipid

Answer: (d)

3. This is a correctly matched pair

(a) Lysosomes – involved in synthesizing amino acids

(b) Microsomes – take part in photosynthesis

(c) Centrosomes – Provides enzymes essential for digestion

(d) Endoplasmic Reticulum – has a role in the formation of a new nuclear membrane while cell divides

Answer: (d)

4. The Endoplasmic Reticulum in fastly dividing cells is

(a) Absent

(b) Not functional

(c) Poorly developed

(d) Highly developed

Answer: (c)

5. The ER and bodies linked with it during ultracentrifugation are separated as a fraction known as

(a) Episome

(b) Polysome

(c) Microsome

(d) Quantasome

Answer: (c)

6. Sarcoplasmic Reticulum is associated with

(a) Hormone synthesis

(b) Protein synthesis

(c) Release of calcium ions from muscle contractions

(d) None of the above

Answer: (c)

7. This is related to the Glycosylation of protein

(a) Lysosome

(b) Peroxisome

(c) Mitochondria

(d) ER

Answer: (d)

8. The transfer vesicle from RER fuse with the region of Golgi complex

(a) Protein Arms

(b) Medial

(c) Cis

(d) Trans

Answer: (c)

9. SER produces

(a) Nucleic Acid

(b) Carbohydrate

(c) Protein

(d) Lipid

Answer: (d)

Endoplasmic Reticulum 

The endoplasmic reticulum is a network of tubes inside a cell and is of two forms, One form has a surface decorated with round organelles called ribosomes which are used to prepare proteins, and is called coarse endoplasmic reticulum while the other has a smooth surface without ribosomes and is used to prepare other substances, is called the smooth endoplasmic reticulum. These membranes form continuous creases that eventually bind to the outer layer of the nuclear envelope. The endoplasmic reticulum is observed in all other eukaryotic cells, except for sperm cells and red blood cells. 

The Function of Endoplasmic Reticulum 

The function of Smooth endoplasmic reticulum: 

1. The Smooth Endoplasmic Reticulum is responsible for the synthesis of essential lipids such as phospholipids and cholesterol which are necessary for the construction of cell membranes.

2. It helps to detoxify certain compounds

3. It helps in carbohydrate metabolism. 

4. Helps in storing and releasing calcium ions, necessary in the contraction of muscle cells and synthesizing male and female hormones in the brain. 

The Function of Coarse/Rough Endoplasmic Reticulum

1. Most of the functions of rough ER are related to protein synthesis because of the round organelles present on top. 

2. Rough endoplasmic reticulum helps in protein folding and quality control. 

3. The second most important function after protein synthesis and protein folding is protein selection. 

4. Rough ER produces antibodies in specific white blood cells. In pancreatic cells, the coarse endoplasmic reticulum produces insulin.

Golgi Body 

The Golgi apparatus or Golgi body named after Camillo Golgi is an organelle that looks like a series of stacked membranes and assists in the processing and packaging of proteins and lipid molecules, especially those intended for export from cells.  

Some of them are renal tubules and some of them are vesicles. The Golgi is very close to the core. It is called the perinuclear body and is also near the endoplasmic reticulum. And as proteins emerge from the endoplasmic reticulum, they go to the Golgi for further processing. 

The Function of Golgi Body 

1. One of the functions of the Golgi is to create new vesicles from the existing Golgi membrane and inject these vesicles with glycoproteins and other substances produced by the Golgi network.

2. The Golgi complex serves as a “traffic police officer” for cells, responsible for directing proteins and lipids to the correct target. 

3. They play a role in the exocytosis of a wide variety of products and proteins, including fragments of zymogen, mucus, lactoprotein, and thyroid hormone. 

4. Other organelles, such as cell membranes and lysozyme, are synthesized by the Golgi complex. 

5. It is also involved in the sulfation of various compounds.

Similarities between Endoplasmic Reticulum and Golgi Body 

The endoplasmic reticulum and the Golgi apparatus are two membrane-bound organelles found in eukaryotes with similar functions. Both the endoplasmic reticulum (ER) and the Golgi apparatus are two components of the cell's endomembrane system. Lysosomes and vesicles are other components of the endomembrane system. There are two types of eukaryotic cells: coarse endoplasmic reticulum and smooth endoplasmic reticulum. The ribosome binds to the rough ER and transports the synthesized polypeptide chain to the rough ER. Post-translational modifications of proteins occur within the ER, thereby maturing the protein. These mature proteins are transported to the Golgi apparatus and transported to their final destination, either by lysosomes, plasma membranes, or excreted from cells into the extracellular environment. Secretion to the extracellular environment is caused by exocytosis.